With recent increase in capacity of network, wavelength multiplexing network using an optical transport network (OTN, ITU-T G.709) technology has been commercialized.
In a protection method of the wavelength multiplexed OTN ring according to the ITU-T G.873.2, when a failure occurs in a certain link (transmission line), both end nodes (transmission apparatuses) of the failure link each detect the failure, and send a switch message to a link on the opposite side of the failure link. The switch message is a message to inform each node of switching a transmission direction of an optical signal.
The switch message has destination information on the other end node of the failure link. A node between both end nodes transfers the message as it is, and the message eventually reaches the other end node of the failure link. When receiving the message, the other end node of the failure link recognizes that the destination is the own node, and performs switching.
In a wavelength multiplexed ring network, the message for this protection operation is sent separately for each wavelength. However, when the number of multiplexed wavelengths increases, the number of switch messages sent among nodes increases, and a processing load in each node increases. This may delay a recovery from the failure.
In view of this, there is a technique called group protection in which, when a failure occurs in a link in the ring network, a plurality of wavelengths are regarded as one group, and one switch message is transmitted in the unit of group. According to this technique, when a failure occurs in the wavelengths in a group, one switch message is transmitted in the unit of group, and thus the transmission directions of optical signals of all the wavelengths are switched together by the end node of the link. This reduces the number of switch messages transmitted and received by the nodes.
Related techniques are disclosed in, for example, Japanese Laid-open Patent Publication Nos. 2013-030884 and 2013-046269.